Why not eliminate the input buffer? (And a big thanks to March Audio!)

[Burning Sounds]

It's the analogue outputs that are 75 ohms. The analogue inputs are spec'd at +4dBm, balanced or unbalanced, 10k Ohm.

I'm no technical expert, so the use of dBm always had me confused.

 

[Panelhead]

And over 20 bucks each if bought new. Last time I checked audio didn't really need connectors good to 2 GHz either - not unless you've got lots of RF floating around for one reason or another.

If I wanted small, I'd probably take a hard look at 5-pin Mini-XLR, two channels in one compact connector and not quite as exotic.

In any case, today I learned that what we are calling XLR actually is just XL, strictly speaking.

Just purchased another batch for 2.00 each on eBay. Free shipping too. But I would pay more if needed.
Audio does not require 2 GHz. Neither does it need -130 dB noise levels.

 

[DonH56]

It's the analogue outputs that are 75 ohms. The analogue inputs are spec'd at +4dBm, balanced or unbalanced, 10k Ohm.

I'm no technical expert, so the use of dBm always had me confused.

+4 dBm referred to 10 k-ohms is about 5 Vrms. Of course they could be mixing up input and output impedances so referring to 75 ohms for +4 dBm (a bit of a mismatch) and 10 k-ohm input impedance (not unusual). I really wonder if they meant dBu and it's a typo.

75-ohm outputs is not unusual though interesting since it is the impedance of a typical audio/AES/video coax cable.

In any event, certainly not a critical thing, wasted enough bandwidth and diverted this thread enough, I have...

 

[AnalogSteph]

I really wonder if they meant dBu and it's a typo.

I think I've seen dBm used for dBu in some old pro audio stuff. dBu = dBm @ 600 ohms after all.

My guess would be that dBm was used first and may haved caused some confusion like that, so dBu was introduced later for disambiguation.

 

[weasels]

Of course, this is only after you've properly installed power crystals throughout your components.

That is the funniest link I've clicked on in a long time.

 

[RayDunzl]

Wasn't ITT a semiconductor/component fabricator in the 1960s/70s in Europe?

Made me look:

https://www.telcomhistory.org/resou...nternational-telephone-telegraph-corporation/

 

[restorer-john]

Made me look:

https://www.telcomhistory.org/resou...nternational-telephone-telegraph-corporation/

I knew there was a German connection:

"The German holding company got ITT involved with the Nazi Party through a banker, Kurt von Schroeder."

 

[DonH56]

I think I've seen dBm used for dBu in some old pro audio stuff. dBu = dBm @ 600 ohms after all.

My guess would be that dBm was used first and may haved caused some confusion like that, so dBu was introduced later for disambiguation.

Duh, I should have made that connection, good catch.

 

[AnalogSteph]

I knew there was a German connection:

"The German holding company got ITT involved with the Nazi Party through a banker, Kurt von Schroeder."

Perhaps more relevant is the fact that ITT Schaub-Lorenz portable radios were quite common in Germany in the 1970s, and they made loudspeaker drivers as well (usually nothing extremely fancy, more like Tesla / Westra competition). These businesses were later sold to Nokia. So if you ever come across some Nokia-branded speaker drivers you'll know how that came about.

 

[restorer-john]

Perhaps more relevant is the fact that ITT Schaub-Lorenz portable radios were quite common in Germany in the 1970s

And Colour TVs here in Australia form the "expensive" retailers. That was the brand link-up I had forgotten- thanks for posting your comment. Was there also a tie-up with Loewe?

 

[Nebbermind]

I think the amp module was designed such that a preamp is no longer necessary.
Having a buffer in front simply allows one to add a pot and turns it into a integrated amp.
Therefore if your connected source has very low output impedance and have no issue with the low impedance of the unbuffered amp module, then go ahead and bypass it.
Otherwise, just leave it alone.
I suspect that without the buffer, the input impedance will vary over the whole audio freq range.

 

[EdW]

. Wasn't ITT a semiconductor/component fabricator in the 1960s/70s in Europe?

Yup. The semiconductor plant was in Freiburg Im Breisgau. Visited it many times in the late 70s, early 80s. Great local wines . .

 

[Panelhead]

Yup. The semiconductor plant was in Freiburg Im Breisgau. Visited it many times in the late 70s, early 80s. Great local wines . .

I think there are some ITT branded C3M fire bottles in my attic. Most there are Siemens.
Think the use was communications.

 

[tifune]

Hello all,

First time post here but long time lurker. I've been following the conversation on Hypex and Purifi amps as closely as I can considering that I have no background in EE whatsoever. With that caveat, it seems that there are benefits to eliminating the input buffer stage as seen in the Amir's Purifi review or in the low gain mode measurements for the Benchmark AHB2 amp. It also seems that there's little difference between discrete "audiophile" op amps and certainly there's debate about whether or not these op amps present any value over stock chips. So, would there be a benefit to eliminating the input buffer if you had a pre-amp that had an appropriately high output voltage? I'm fortunate enough to own one, the Benchmark DAC3, which by default outputs 24 dBu (12 volts RMS).

So, it's been awhile now, are you still happy with this setup? Any unexpected +/-'s ? I'm thinking of doing the same thing with a VTV Purifi unit, probably using one of the Topping pre's. I don't expect any miracles, but if I can get an extra 5dB SINAD and a HP amp in one cheap package why not try it?

 

[yodog]

Reading the OPs post makes me seriously want to buy a high powered amplifier from March Audio. Wonder how much it is to ship to Southern California...

 

[stoyania]

Reading the OPs post makes me seriously want to buy a high powered amplifier from March Audio. Wonder how much it is to ship to Southern California...

hmmm...I thought March Audio was banned for delivering amps that didn't meet the advertized specs and not resolving the issues afterwards.
Or did I misunderstand?

 

[maverickronin]

hmmm...I thought March Audio was banned for delivering amps that didn't meet the advertized specs and not resolving the issues afterwards.
Or did I misunderstand?

Nah, his specs were basically fine.

He was banned because he always had to have the last word in every argument causing threads to degenerate into uselessness and antagonized Amir and the mods when they asked him to stop.

 

[Kachda]

Reading the OPs post makes me seriously want to buy a high powered amplifier from March Audio. Wonder how much it is to ship to Southern California...

80 bucks or so is what i paid for shipping to New York

edit: 85 bucks actually.

 

[yodog]

80 bucks or so is what i paid for shipping to New York

edit: 85 bucks actually.

how do you like (or dislike) the amp?

 

[Kachda]

how do you like (or dislike) the amp?

I have no complaints. Runs well without any problems for me. And Alan is very responsive to any queries.